Conventionally, when extending through a work and performing threading and helical milling, electric discharge machining is performed by using an electrode in which an electrode for rough machining and an electrode for finish machining are coaxially arranged to be integrated as disclosed, for example, in Japanese Unexamined Utility Model Application Publication S61-5528.
For example, as an example of the integral electrode that coaxially includes the rough machining electrode and the finish machining electrode, one illustrated in FIG. 6 is present.
FIG. 6(a) illustrates an electrode for forming a through female screw by the electric discharge machining and a work, in which a pilot hole with a size for the electrode to enter is formed in the work and circular rocking machining is performed while gradually enlarging the pilot hole laterally in a state where the electrode is inserted into the pilot hole of the work to transfer the shape of the electrode, thereby forming the female screw inside the work. Then, after finishing this rough machining, the electrode is returned to a center position and is further moved in a Z direction by a constant amount, and then the electric discharge machining for the finish machining is performed again.
The third electric discharge machining is performed depending on the situation to repeat the finish machining for improving accuracy of the female screw in some cases.
FIG. 6(b) illustrates an electrode for forming a through helical-gear female mold by the electric discharge machining and a work, in which a pilot hole with a certain size is formed in the work and the electric discharge machining is performed while rotating the electrode by a constant rotation angle at the same time as the electrode is lowered in the Z direction to transfer the shape of the electrode, thereby forming the helical-gear female mold inside the work. Then, after finishing this rough machining, the electrode is lowered by a constant rotation angle in the Z direction without performing the electric discharge, and thereafter the electric discharge machining for the finish machining is performed again with the next electrode part. The third electric discharge machining is performed depending on the situation to repeat the finish machining for improving accuracy of the female mold in some cases.
In this manner, in the case of performing machining of extending through the work, there is a form in which each of coaxially-formed electrode parts individually performs the electric discharge machining in order, for example, as a rough machining electrode, a finish machining electrode 1, and a finishing machining electrode 2 to machine the work.
Patent document 1: Japanese Unexamined Utility Model Application Publication S61-5528 FIG. 3